1. Field of the Invention
This invention relates generally to magnetic storage systems, and more particularly, to air bearing sliders having air bearing pads shaped to provide a desired flying height profile.
2. Description of Related Art
A magnetic storage system typically includes one or more magnetic disks with at least one data recording surface having a plurality of concentric tracks for storing data. A spindle motor and spindle motor controller rotate the disk(s) at a selected rotations per minute (rpm) such that at least one read/write transducer or "head" per recording surface can read data from or write data to each recording surface. The data read or written from each recording surface is processed by a read/write channel. The transducer is supported by an air bearing slider which has a top surface attached to an actuator assembly via a suspension, and a bottom surface having an air bearing design of a desired configuration to provide favorable flying height characteristics. During the operation of the magnetic storage device, the air bearing slider is positioned in close proximity above the desired data track by an actuator assembly. The movement of the actuator assembly above the disk surface is controlled by a servo system.
In magnetic recording technology, it is continually desired to improve the areal density at which information can be recorded and reliably read. Because the recording density of a magnetic storage system is limited by the distance between the transducer and the recording surface of the disk, it is generally desirable to design an air bearing slider to "fly" as closely as possible to the recording surface of the disk while avoiding physical impact with the disk. Smaller spacings, or "flying heights" allow the transducer to distinguish between the magnetic fields emanating from closely spaced regions on the disk.
The flying height of the slider is typically affected as the actuator arm is moved radially to access different data tracks from the inner-diameter (ID) radius to the outer-diameter (OD) radius of the disk surface. This is primarily due to differences in the linear velocity of the disk at differing radii. In effect, the air bearing slider flies at different heights at differing radii. A slider typically flies higher as velocity increases. However, a slider also experiences changes in flying height due to variations in skew. Skew is a measure of the angle formed between the longitudinal axis of the slider and the direction of disk rotation as measured in a plane parallel to the disk. Skew varies in a magnetic storage system that includes a rotatory actuator as the suspension and attached slider move in arcuate path across the disk surface. For rotary actuators, the slider typically has a more positive skew at the OD, a more negative skew at the ID, and a substantially zero skew at the MD. Skew also varies, to a lesser degree, in a linear actuator magnetic storage system when a resiliently mounted slider moves in response to forces exerted upon it. For sliders positioned by either type of actuator, non-zero skew values result in a slider being pressurized less and therefore flying lower.
Taking into consideration that the velocity and skew of the slider varies across the different zones of the disk surface, the flying height profile is typically higher at the middle-diameter (MD) zone of the disk surface and lower around the inner-diameter (ID) and outer-diameter (OD) zones of the disk surface. But for many magnetic storage systems, it is desirable to design an air bearing slider that maintains a generally constant "flying height" between the read/write head the disk surface across all data zones, from the inner-diameter (ID) radius to the outer-diameter (OD) radius of the disk.
FIG. 1A represents a conventional slider 100 having a tri-pad air bearing design. The air bearing surface is formed by three air bearing pads 104, 106, and 108. Pads 104 and 106 are formed substantially adjacent to the leading edge 111 of slider 100 and pad 108 is formed substantially adjacent to the trailing edge 110 of slider 100. Stepped or ramped surfaces 114 and 116 are formed along the leading edge of air bearing pads 104 and 106, respectively.
FIG. 1B illustrates the flying height profile of slider 100. Generally, a flying height profile represents the flying height of a slider as the slider flies from the ID radius to the OD radius of the disk surface. The flying height profile 160 is a relatively steep profile with the lower flying heights at the ID and OD radii of the disk surface and the highest flying height at the MD radius of the disk surface.
Under certain circumstances, it may be desirable to adjust the flying height profile. For example, certain magnetic storage systems may operate more efficiently when the flying height is lowest at the MD while slightly higher at the OD and ID. One approach to adjusting the flying height profile of a slider is to provide air bearing pads or rails having diverging side edges as described in patent application Ser. No. 08/731,606 entitled "Method and Apparatus for Providing Diverging Rail Edge Geometry for Air Bearing Slider," which is assigned to the same assignee as the present invention. By providing a slider having a wider downstream area than upstream area, relatively constant pressure can be maintained as the skew angle varies while the air flow changes direction.
FIG. 2 illustrates an air bearing pad 200 that may be used in various air bearing designs. For example, one or more rectangular air bearing pads (including associated compression feature) shown in FIG. 1 may be replaced with one or more air bearing pads 200 (including associated compression feature 210). The diverging region for pad 200 is downstream from the the leading edge of pad 200.
Consequently, the pressure build up resulting from pad 200 occurs collinearly with the direction of air flow under skewed conditions. In other words, only the area downstream from tapered region 210 pressurizes. Note that areas 202 away from pressurization zone 201 do not pressurize and therefore do not contribute to the air bearing. FIGS. 2B-2D illustrate the various air flow conditions (i.e., ID air flow, MD air flow, and OD air flow) and how the pressurization zone 201 changes with respect to the direction of the air flow. As the air flow changes direction, the pressure peak 214 shifts with the air flow.
FIGS. 2E-2G show the normalized pressure contours 215-217 taken along the width of the trailing edge 240 of pad 200 for the various conditions. FIG. 2E corresponds to an ID air flow condition, FIG. 2F corresponds to an MD air flow condition, and FIG. 2G corresponds to an OD air flow condition. Generally, pressure peak 214 is shifted toward pressurization zone 201 while the portion 202 remains at or near ambient pressure.
FIG. 2H illustrates a flying height profile for a tri-pad air bearing design incorporating three air bearing pads 200 having diverging side rails. Although flying height profile 260 is relatively flat, the flying height is lowest near the MD. As mentioned above, this particular flying height profile may be desirable for certain magnetic storage systems.
The flying height profiles shown in FIGS. 1B and 2H may not be suitable for certain magnetic storage system configurations. For example, magnetic storage systems that operate in a contact start-stop mode may include a textured landing zone located at either the ID or OD zone of a disk surface. The textured landing zone may require that the slider fly slightly higher over the landing zone than the data zone to avoid the bumps or protrusion in the textured zone rather than a flying relatively flat across the various zones on the disk surface. Thus, there is a need for an air bearing slider having air bearing pads and/or rails that can be shaped to provide the desired flying height profile.